1. Field of the Invention
The present invention relates generally to a supply-and-demand control system for use in local power systems, each having power generation units and load units. More particularly, the invention relates to a supply-and-demand control system of distributed and coordinated type.
2. Description of the Related Art
In most commercial power systems, it is important to control the power demand and supply in good balance in the local power systems installed at the individual power consumers in order to achieve stable power supply to each power consumer. To achieve stable power supply, it is advisable to use positively variable power resources such as solar generation units and wind generation units. Control techniques that can drive electrical loads in energy-saving mode and can stabilize the power supply to the power consumers are demanded.
The loads of various electric apparatuses that are used in each power consumer are important equipment that governs production activities. In view of this, it is difficult to accomplish a power control at the load side, which is known as “demand-side control (DSC)” or “demand-side management (DSM)”. Hence, in practice, the demand and supply of power are controlled by performing a minute control of power at the power generation equipment, thereby absorbing changes in the demand and supply. Inevitably, the supply-and-demand control system used is complicated, increasing the system cost and the engineering cost.
Power supply control and communication systems have been proposed, each designed to control the demand and supply of power in a group of electric equipment. See, for example, Jpn. Pat. Appln. KOKAI Publication No. 10-094199. The system disclosed in this document comprises an equipment management server and a supply-and-demand monitor center. The server registers and manages the individual apparatuses. The supply-and-demand monitor center controls the demand and supply of power. More precisely, the supply-and-demand monitor center calculates the electricity that can be consumed in the entire equipment and allows each apparatus to use a specific amount of power, thus accomplishing DSC.
The system disclosed in the above-identified document needs not only the equipment management server and the supply-and-demand monitor center, but also a communication system. It is inevitably a huge system as a whole and requires a high installation cost. Further, its overall configuration must be changed every time new electric equipment is introduced or the superannuated equipment is discarded. Both the engineering cost and the maintenance cost will inevitably increase.
As a system that performs the supply-and-demand control of power, a supply-and-demand control system applied to a microgrid is proposed (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2008-104269.) The microgrid is a system includes regional power supplies that can generate power by itself and operate independently of the power supply system supplying power to general power consumers, in order to reduce the emission of carbon dioxide (CO2). Note that the regional power supplies are, for example, fuel cells, solar generation units and wind generation units. The microgrid is a system that links these regional power supplies and controls the power supply. Thus, the regional power supplies can be effectively used when the commercially available power system breaks down or when the power demanded is small. The supply-and-demand control system used in the microgrid has a supply-and-demand server that registers both the power supply apparatuses and the load apparatuses and controls the outputs of the power supply apparatuses in accordance with the power consumed at the load apparatuses.
The supply-and-demand control system used in the microgrid is, however, a huge system that include fuel cells, solar generation units, wind generation units, etc., installed in cities, towns, villages and districts. Its installation cost is very high. Moreover, its engineering cost and its system maintenance cost may increase if its configuration is changed, because the server alone controls the demand and supply of power at all individual apparatuses.